Father's Legacy is the last treasure obtainable in Sly Cooper: Age of Thieves, and it the only treasure found in Sly's Father's Time. It can only be obtained once all of the other treasures have been found. Doing so unlocks the arcade machine in the final hideout.
"Sly's Father, Conner, was arguably one of the finest thieves who ever lived, and among the greatest of the Cooper Clan. To Sly, he is one of the biggest role models, and because of his untimely death, Sly had to rely only on his teachings. This broken piece of a portrait finally manages to show Conner's true face, and his resemblance to Sly is quite touching, to say the least."
It is located within the ruins of the Cooper family home. Sly is, understandably, the only character who can reach this treasure. Once he does so, the treasure will instantly go to the hideout. Normally, when Sly reaches the Cooper household, a cutscene starts. However, the cutscene will only begin after the treasure has been picked up.